Lubricant for electrophotography, lubricant applying unit, process cartridge, and image forming apparatus

ABSTRACT

An lubricant for electrophotography is applied to a latent image carrier that is supplied with toner having a sphericity of 0.94 or more. The lubricant for electrophotography is added with an inorganic additive having the following relationship:
 
2 Y /1000≦ X≦Y /10
where Y is a toner particle size (micrometer), and X is an inorganic additive particle size (micrometer).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document incorporates by reference the entire contents ofJapanese priority document, 2003-414090 filed in Japan on Dec. 12, 2003.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a lubricant for electrophotography usedin an electrostatic duplicating process for development by supplyingtoner to a latent image carrier that carries a latent image, and to alubricant applying unit, a process cartridge, and an image formingapparatus.

2) Description of the Related Art

Electrophotographic color image forming apparatuses are widespreadrecently, and digitized images are easily available. Under thesecircumstances, higher definition is required for printed images. Higherresolution and gradation of images are studied, and improvement of tonerused to visualize a latent image is also studied. In order to form ahigh-definition image, it is also studied to obtain a higher degree ofsphericity and a smaller particle size of toner.

For example, pulverized spherical toner particles having a specifiedparticle size distribution are described in Japanese Patent ApplicationLaid-Open Publication No. Hei 11-12253, Japanese Patent ApplicationLaid-Open Publication No. Hei 2-284158, Japanese Patent ApplicationLaid-Open Publication No. Hei 3-181952, and Japanese Patent ApplicationLaid-Open Publication No. Hei 4-162048. Japanese Patent ApplicationLaid-Open Publication No. Hei 5-72808 discloses a method of obtainingspherical toner having a small particle size through suspensionpolymerization. Japanese Patent Application Laid-Open Publication No.Hei 9-15902 discloses a method of obtaining spherical toner having asmall particle size by mixing a,binder resin with a colorant in asolvent without water therein and dispersing the mixture into an aqueoussolvent containing a dispersion stabilizer. Japanese Patent ApplicationLaid-Open Publication No. Hei 11-133668 discloses a method of obtainingspherical toner having a small particle size by mixing a binder resinpartially containing modified resin with a colorant in an organicsolvent, and dispersing the mixture into an aqueous solvent to allowpolyaddition reaction of the modified resin to be performed. By usingsuch toner, improved image quality and improved fluidity are obtained.

To improve image quality, it is necessary to remove toner remaining onthe surface of a photosensitive element as much as possible after atoner image is transferred. Particularly, since spherical toner is easyto roll, the toner enters between a cleaning blade and thephotosensitive element upon cleaning of the photosensitive element(latent image carrier). Some toner passes under the cleaning blade andremains on the photosensitive element, which may cause an abnormal imagesuch as surface fog to occur. Various examinations to solve this problemare carried out.

For example, Japanese Patent Application Laid-Open Publication No. Hei11-184340 discloses a method of forming an electrophotographic imageusing a cleaning member for cleaning toner remaining on a photosensitiveelement with an elastic rubber blade. In the method, by making zincstearate as a lubricant contain in toner by a range from 0.01% to 0.5%to the weight of the toner, a frictional coefficient of thephotosensitive element is reduced and cleaning efficiency with theelastic rubber blade is increased.

Japanese Patent Application Laid-Open Publication No. 2002-287567discloses an image forming device that forms an electrostatic latentimage on a photosensitive element, visualizes the electrostatic latentimage as a toner image with toner containing a mold release agent,transfers the toner image to a recording medium directly or through anintermediate transfer element, and fixes the toner image on therecording medium. In the image forming device, by applying zinc stearateas a lubricant to the photosensitive element, a frictional coefficientof the photosensitive element is reduced and cleaning efficiency withthe elastic rubber blade is increased.

However, in the invention of Japanese Patent Application Laid-OpenPublication No. Hei 11-184340, if zinc stearate is added to the toner,the zinc stearate may be unevenly distributed over the photosensitiveelement depending on the status of an image to be developed. In aportion with a small amount of zinc stearate, some toner particles passunder the elastic rubber blade to remain on the photosensitive element.In the invention of Japanese Patent Application Laid-Open PublicationNo.,2002-287567, if an image with a large image area therein is formedin image mode, the zinc stearate adheres to the toner particles, and alarge amount of zinc stearate are taken away. Thereby, the distributionof the zinc stearate on the photosensitive element becomes uneven, andin a portion with a small amount of the zinc stearate, some of the tonerparticles pass under the cleaning blade to remain on the photosensitiveelement. There is a problem, which is common to the inventions ofJapanese Patent Application Laid-Open Publication No. Hei 11-184340 and2, such that in an initial stage of use of a new photosensitive element,only a small amount of zinc stearate is present on the photosensitiveelement, which causes insufficient removal of toner remaining on thephotosensitive element.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least the aboveproblems in the conventional technology.

A lubricant for electrophotography according to one aspect of thepresent invention is applied to a latent image carrier to which tonerhaving a sphericity of equal to or more than 0.94 is supplied. Aninorganic additive is added to the lubricant, and the inorganic additivesatisfies2Y/1000≦X≦Y/10where Y is a particle size of the toner in micrometer, and X is aparticle size of the inorganic additive in micrometer.

A lubricant applying unit according to another aspect of the presentinvention, which applies a lubricant for electrophotography to a latentimage carrier, includes a brush roller that rotates around a rotationalaxis, and is in contact with the latent image carrier. Toner having asphericity of equal to or more than 0.94 is supplied to the latent imagecarrier. An inorganic additive is added to the lubricant, and theinorganic additive satisfies2Y/1000≦X≦Y/10where Y is a particle size of the toner in micrometer, and X is aparticle size of the inorganic additive in micrometer. The lubricant isa molded lubricant that is molded as a solid block, and the brush rollerslides along, and scrapes off the molded lubricant so that the lubricantis applied to the latent image carrier.

A process cartridge according to still anther aspect of the presentinvention includes a latent image carrier; at least one of

-   -   a charging unit that causes a charging member to contact or to        be close to the latent image carrier to charge the latent image        carrier, a developing unit that deposits toner on a latent image        on the latent image carrier to develop the latent image with the        toner, and a cleaning unit that cleans the toner remaining on        the latent image carrier with a cleaning blade; and a lubricant        applying unit that applies a lubricant for electrophotography to        the latent image carrier. The lubricant applying unit includes a        brush roller that rotates around a rotational axis, and is in        contact with the latent image carrier. Toner having a sphericity        of equal to or more than 0.94 is supplied to the latent image        carrier. An inorganic additive is added to the lubricant, and        the inorganic additive satisfies        2Y/1000≦X≦Y/10        where Y is a particle size of the toner in micrometer, and X is        a particle size of the inorganic additive in micrometer. The        lubricant is a molded lubricant that is molded as a solid block,        and the brush roller slides along, and scrapes off the molded        lubricant so that the lubricant is applied to the latent image        carrier.

An image forming apparatus according to still another aspect of thepresent invention includes a process cartridge that includes a latentimage carrier; at least one of a charging unit that causes a chargingmember to contact or to be close to the latent image carrier to chargethe latent image carrier, a developing unit that deposits toner on alatent image on the latent image carrier to develop the latent imagewith the toner, and a cleaning unit that cleans the toner remaining onthe latent image carrier with a cleaning blade; and a lubricant applyingunit that applies a lubricant for electrophotography to the latent imagecarrier. The lubricant applying unit includes a brush roller thatrotates around a rotational axis, and is in contact with the latentimage carrier. Toner having a sphericity of equal to or more than 0.94is supplied to the latent image carrier. An inorganic additive is addedto the lubricant, and the inorganic additive satisfies2Y/1000≦X≦Y/10where Y is a particle size of the toner in micrometer, and X is aparticle size of the inorganic additive in micrometer. The lubricant isa molded lubricant that is molded as a solid block, and the brush rollerslides along, and scrapes off the molded lubricant so that the lubricantis applied to the latent image carrier.

An image forming apparatus according to still another aspect of thepresent invention includes a lubricant applying unit that applies alubricant for electrophotography to a latent image carrier. Thelubricant applying unit includes a brush roller that rotates around arotational axis, and is in contact with the latent image carrier. Tonerhaving a sphericity of equal to or more than 0.94 is supplied to thelatent image carrier. An inorganic additive is added to the lubricant,and the inorganic additive satisfies2Y/1000≦X≦Y/10where Y is a particle size of the toner in micrometer, and X is aparticle size of the inorganic additive in micrometer. The lubricant isa molded lubricant that is molded as a solid block, and the brush rollerslides along, and scrapes off the molded lubricant so that the lubricantis applied to the latent image carrier.

The other objects, features, and. advantages of the present inventionare specifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross section of a main part near a contactportion between a cleaning blade and a photosensitive element when alubricant for electrophotography is applied thereto;

FIG. 2 is an enlarged cross section of the main part when the lubricantfor electrophotography is not applied thereto;

FIG. 3 is a schematic diagram of the whole of a compact-size full colorprinter;

FIG. 4 is a schematic diagram of a configuration of a process cartridge;

FIG. 5 is a flowchart of an operation of a new-latent-image-carrierdetector;

FIG. 6A and FIG. 6B are schematic diagrams of shapes of toner, in whichFIG. 6A is a diagram for explaining a shape factor SF-1 and FIG. 6B is adiagram for explaining a shape factor SF-2;

FIG. 7A and FIG. 7B are schematic diagrams of outline shapes of toner,in which FIG. 7A is a diagram of external appearance of the toner andFIG. 7B is a cross section of the toner;

FIG. 8 is a schematic diagram of toner;

FIG. 9 is a diagram of a relationship between the particle size of anadditive added to a molded lubricant and the soil of a charging roller;

FIG. 10 is a diagram of changes in the frictional coefficient of thephotosensitive element caused by application of the lubricant theretowhen sheets of paper are actually passed;

FIG. 11 is a diagram for explaining how to measure the frictionalcoefficient of the photosensitive element; and

FIG. 12 is a diagram of an application time of the lubricant and achange with time in the frictional coefficient of the photosensitiveelement.

DETAILED DESCRIPTION

Exemplary embodiments of a lubricant for electrophotography, a lubricantapplying unit, a process cartridge, and an image forming apparatusaccording to the present invention are explained in detail below withreference to the accompanying drawings.

In an embodiment of the present invention, silica is added to alubricant for electrophotography (hereinafter, “lubricant”) as aninorganic additive that satisfies the following relationship.2Y/1000≦X≦Y/10  (1)where Y is a volume-average particle size of toner (μm), and X is aparticle size of silica (μm)

As the inorganic additive to be added, an inorganic substance such assilica, titania, alumina, magnesia, zirconia, ferrite, and magnetite canbe used alone or in combination if the particle size satisfies therelationship of expression (1).

An amount of addition of the inorganic additive to a main component ofthe lubricant ranges preferably from 1 to 30 weight percent (wt. %). Ifthe amount of addition exceeds 30 wt. %, it is difficult to mold thelubricant as a solid block, i.e., to form a molded lubricant, which isnot preferable. Furthermore, if the amount of addition is less than 1wt. %, adequate cleaning performance cannot be obtained, which is alsonot preferable.

As the lubricant used for the molded lubricant, a lubricant obtained inthe following manner is used. The lubricant is obtained by adding theinorganic additive explained later to zinc stearate that is a maincomponent and melting and solidifying the substance obtained byaddition. Examples of a main component of the lubricant are aliphaticacid metal salts which are preferably melted and solidified, such aslead oleate, zinc oleate, copper oleate, zinc stearate, cobalt stearate,iron stearate, copper stearate, zinc palmitate, copper palmitate, andzinc linoleate. Furthermore, the examples are fluorine resins which arepreferably molded, such as polytetrafluoroethylene,polychloro-trifluoroethylene, polyvinylidene fluoride, polytrifluorochloro ethylene, dichloro-difluoroethylene,tetrafl-uoroethylene-ethylene copolymer, andtetrafluoroethylene-oxafluoropropylene copolymer. Particularly, metalstearate that is most effective in reduction in friction of thephotosensitive element is preferably used, and zinc stearate is morepreferably used.

The shape of toner for use is set to 0.94 or more in sphericity. Thesphericity is defined that the circumferential length of a circle havingarea the same as the area of a projected image of a particle is dividedby the circumferential length of the projected image of the particle.Therefore, if toner is close to perfect sphericity, the sphericityreaches a value near unity. The degree of sphericity of the toner havingsuch a degree of sphericity is controlled by being strongly stirred inthe process of removing organic solvent in the method of manufacturingtoner, which is explained later. It is also possible to obtain tonerhaving high sphericity by subjecting the toner manufactured through drymilling to spherical processing. The spherical processing of the tonermanufactured by the dry milling is roughly divided into a thermal methodand a mechanical method. The thermal method includes a method ofperforming the spherical processing by atomizing toner particles withthermal current by an atomizer. The mechanical method includes a methodof performing the spherical processing by charging toner together with amixing medium, such as glass having light specific gravity, into a mixersuch as a ball mill, and stirring them. However, in the thermal method,toner particles agglomerate with one another to produce toner particleshaving a large particle size, while in the mechanical method, finepowder is produced. Therefore, both of the methods require the processof re-classification.

By adding the inorganic additive to the lubricant, stable cleaningperformance is obtained. This mechanism can be explained as follows as aresult of observing the mechanism with a microscope. FIG. 1 is anenlarged cross section of a main part near a contact portion between acleaning blade and a photosensitive element when the lubricant accordingto the embodiment is applied. FIG. 2 is an enlarged cross section of themain part near the contact portion between the cleaning blade and thephotosensitive element when the lubricant according to the embodiment isnot applied. By referring to FIG. 1, a cleaning blade 15 a is in contactwith the surface of a photosensitive element 5, and cleaning isperformed by scraping toner particles T remaining on the photosensitiveelement 5 from the surface thereof. The lubricant is supplied by a brushroller (not shown) to the photosensitive element 5 in the upstream sidein a direction of rotation thereof from the contact portion between thecleaning blade 15 a and the photosensitive element 5. The cleaning blade15 a is curved downwardly near the contact portion, and a space betweenthe photosensitive element 5 and the cleaning blade 15 a is gettingnarrower toward the contact portion. In the space, a portion that isnarrower than the size of the toner particle T is defined as a region C.

If the inorganic additive is not added to the lubricant, as shown inFIG. 2, the toner particle T enters the region C and passes under thecleaning blade 15 a as if the toner particle T is pulled toward thedirection of rotation of the photosensitive element 5. In this case, thetoner particles T remain on the surface of the photosensitive element 5without being cleaned. On the other hand, if the inorganic additive isadded to the lubricant, as shown in FIG. 1, inorganic additive particleshaving a smaller particle size than that of the toner particle T enterthe region C. The region C is filled with the inorganic additiveparticles, and the toner particles T are thereby prevented from enteringthe region C. The region C filled with the inorganic additive particlesin the above manner serves as a roll of a “bank” for stopping the tonerparticles T. In this case, almost all of the toner particles T isremoved from the photosensitive element 5 with the cleaning blade 15 a(see Example 1).

The image forming apparatus using the lubricant according to theembodiment is explained below with reference to the attached drawings. Afour-drum tandem system and a direct transfer system such that atransfer paper and the photosensitive element (latent image carrier) arein direct contact with each other is exemplified in this embodiment.However, any imaging system such as an intermediate transfer belt systemand a revolver type development system may be employed if the imagingsystem is such that a lubricant is applied to the photosensitive elementand the lubricant is the one explained above.

FIG. 3 is a schematic diagram of the whole of a compact-size full colorprinter. The main body of the image forming apparatus 1 (hereinafter,“main body 1”) includes process cartridges 2A, 2B, 2C, and 2D that havethe photosensitive elements 5 being four image carriers, and that aredetachably attached to the main body 1, respectively. A transfer device3 is arranged in a substantially center of the main body 1. The transferdevice 3 includes a transfer belt 3 a wound around between a pluralityof rollers so as to be rotatable in the direction of arrow A. Thephotosensitive elements 5 respectively provided in the processcartridges 2A, 2B, 2C, and 2D are arranged along the upper surface ofthe transfer belt 3 a so as to be in contact with the transfer belt 3 a.Developing devices 10A, 10B, 10C, and 10D each of which includes tonerof a different color are arranged corresponding to the processcartridges 2A, 2B, 2C, and 2D, respectively. A writing unit 6 isprovided above the process cartridges 2A, 2B, 2C, and 2D, and adouble-sided unit 7 is provided under the transfer belt 3 a . Areversing unit 8 is provided in the left side of the main body 1. Thereversing unit 8 reverses the transfer paper P after an image is formedthereon to discharge the transfer paper P reversed or to convey thetransfer paper P reversed to the double-sided unit 7. A fixing device 9that fixes the image on the transfer paper P is provided between thetransfer belt 3 a and the reversing unit 8. A paper reverse dischargingpath 20 is branched on the downstream side of the fixing device 9 in atransfer-paper conveyance direction. The transfer paper P conveyed tothe paper reverse discharging path 20 is discharged onto a paperdischarge tray 26 by a discharging roller pair 25. A paper feed portionincluding paper feed cassettes 11 and 12 is arranged in the lower sideof the main body 1. The paper feed cassettes 11 and 12 are verticallyarranged in two stages and have transfer paper P of different sizes. Amanual feed tray 13 is provided in the right side of the main body 1 soas to be open in the direction of arrow B. By opening the manual feedtray 13, a paper can be fed manually therethrough.

The developing devices 10A, 10B, 10C, and 10D have the sameconfiguration as one another but only colors of toner to be used aredifferent from one another. More specifically, the developing device 10Auses toner of magenta, the developing device 10B uses toner of cyan, thedeveloping device 10C uses toner of yellow, and the developing device10D uses toner of black. Each of the developing devices 10A, 10B, 10C,and 10D includes a developing roller provided opposite to thephotosensitive element 5, a screw that conveys and stirs developer, anda toner density sensor. The developing roller includes a sleeve that isprovided outside the developing roller and can freely rotate, and amagnet fixed to the inside of the developing roller. Toner is suppliedto the developing device by a toner supply device according to theoutput of the toner density sensor. In the embodiment, a two-componentdeveloper consisting of toner and carrier is used as the developer.Carrier itself as a core material or carrier with a coating layer coatedon a core material is usually used as the carrier. A material used asthe core material includes ferrite and magnetite. The particle size ofthe core material ranges from 20 to 65 micrometers, and preferably fromabout 30 to about 60 micrometers. Resin used for forming the coatinglayer includes styrene resin, acrylic resin, fluororesin, siliconeresin, a mixture thereof, or copolymer thereof. The coating layer can beformed in known methods. For example, it can be formed by coating thesurface of the core material with resin in an atomizing method or adipping method.

The writing unit 6 includes four laser-diode light sources prepared forthe colors, a pair of polygon scanners having a six-facet polygon mirrorand a polygon motor, fθ lenses arranged in light paths of the respectivelight sources, lenses such as a long-local-length cylindrical lens, andmirrors. A laser beam emitted from the laser diode is polarized andscanned with the polygon scanner and is radiated onto the photosensitiveelement 5.

The double-sided unit 7 includes a pair of conveying guide plates 45 aand 45 b, a plurality of conveying roller pairs 46 (four pairs in thiscase). In a double-sided image forming mode in which images are formedon both surfaces of the transfer paper P, an image is formed on one ofthe surfaces, the transfer paper P with the image thereon is conveyed toa paper reverse conveying path 54 of the reversing unit 8, switched backtherein, and conveyed to the double-sided unit 7. The double-sided unit7 receives the transfer paper P (reversed) switched back, and conveys ittoward the paper feed portion.

The reversing unit 8 includes a plurality of conveying roller pairs 60,and the paper reverse conveying path 54 formed with a plurality ofconveying guide plate pairs 61. As explained above, the reversing unit 8reverses the transfer paper P and sends the transfer paper P reversed tothe double-sided unit 7 for forming images on both surfaces of thetransfer paper P, or discharges the transfer paper P with an imageformed, in the direction as it is, to the outside of the machine orreverses the transfer paper P and discharges the transfer paper Preversed to the outside of the machine.

The paper feed portion includes the paper feed cassettes 11 and 12, andpaper separating units 55 and 56 for separating sheets of the transferpaper P one by one for feeding are provided near paper feeding ports,respectively.

The process cartridges 2A, 2B, 2C, and 2D are units having the sameconfiguration as one another. The process cartridge 2A forms an imagecorresponding to magenta, the process cartridge 2B forms an imagecorresponding to cyan, the process cartridge 2C forms an imagecorresponding to yellow, and the process cartridge 2D forms an imagecorresponding to black. FIG. 4 is a schematic diagram of a configurationof the process cartridge. Each of the process cartridges 2A, 2B, 2C, and2D includes a charging unit 14, a cleaning unit 15, the photosensitiveelement 5, and a lubricant applying unit 17. The charging unit 14 makesa charging roller 14 a as a charging member come in contact with thephotosensitive element 5 and charges it. The cleaning unit 15 includes acleaning blade 15 a for cleaning toner remaining on the photosensitiveelement 5 by contacting the photosensitive element 5. The photosensitiveelement 5 rotates and has an electrostatic latent image formed thereon.The lubricant applying unit 17 includes a brush roller 17 a that is madeto rotate around a rotational axis thereof arranged in parallel to therotational axis of the photosensitive element 5 and applies thelubricant onto the photosensitive element 5.

The process cartridge includes at least one of the charging unit, thedeveloping device that develops the latent image on the photosensitiveelement 5 with toner, and the cleaning unit. The process cartridge alsoincludes the photosensitive element 5 and the lubricant applying unit17. The process cartridge is not limited to the one according to theembodiment if it is detachably attached to the main body 1. Byconfiguring the process cartridge in such a manner as explained above,the life of the photosensitive element 5 accommodated in the processcartridge can be prolonged. For maintenance, the process cartridge issimply replaced with a new one, which allows improved convenience.

The charging roller 14 a of the charging unit 14 is conductive, andcharges the photosensitive element 5 by applying a DC and/or an ACvoltage thereto. A charging-roller cleaning brush 14 b is provided incontact with the charging roller 14 a so as to clean the surface of thecharging roller 14 a.

The cleaning unit 15 moves toner scraped off from the surface of thephotosensitive element 5 with the cleaning blade 15 a , to a tonerconveying auger 15 d through rotation of the brush roller 17 a. Wastetoner recovered to the toner conveying auger 15 d is conveyed to a wastetoner container 18 as shown in FIG. 3.

The lubricant applying unit 17 is included in each of the processcartridges 2A, 2B, 2C, and 2D. The lubricant applying unit 17 includes amolded lubricant 17 b obtained by molding the lubricant to an elongatedrectangle, and the brush roller 17 a for scraping the lubricant bycoming in contact with the molded lubricant 17 b and applying it to thesurface of the photosensitive element 5. The lubricant applying unit 17also includes a brush roller scraper 17 c for removing the tonerdeposited on the brush roller 17 a, a pressure spring 17 d that pushesthe molded lubricant 17 b against the brush roller 17 a at predeterminedpressure, and a new-latent-image-carrier detector (not shown) thatdetects whether a latent image carrier or the photosensitive element 5is used for the first time (whether the photosensitive element 5 isnew). Although the lubricant applying unit 17 is included in each of theprocess cartridges 2A, 2B, 2C, and 2D, it may be directly included inthe main body 1.

The brush roller 17 a has a shape of extending in the direction of therotational axis of the photosensitive element 5. The pressure spring 17d biases the brush roller 17 a toward the molded lubricant 17 b so as torun out of almost all the molded lubricant 17 b . The brush roller 17 ascrapes off the molded lubricant 17 b , so that the thickness of themolded lubricant 17 b is reduced with time. However, the moldedlubricant 17 b is biased by the pressure spring 17 d , and is therebykept in contact with the brush roller 17 a. The lubricant is scrapedfrom the molded lubricant 17 b , and the lubricant scraped is applied tothe photosensitive element 5.

The molded lubricant 17 b is pushed against the brush roller 17 a by thepressure spring 17 d at a pressure of 200 meter-newtons or moreincluding the dead weight. With the increase in the pushing force, thelubricant scraped from the molded lubricant 17 b by the brush roller 17a increases, and the amount of the lubricant applied to thephotosensitive element 5 is increased, which allows the frictionalcoefficient of the photosensitive element 5 to be efficiently reduced.

The brush roller 17 a is made to rotate in the direction of rotation ofthe photosensitive element 5 at a portion in contact with thephotosensitive element 5. A peripheral speed ratio (peripheral speed ofphotosensitive element/peripheral speed of brush roller) between thebrush roller 17 a and the photosensitive element 5 is set to 1.0. Bymaking the brush roller 17 a to rotate following rotation ofphotosensitive element 5, the lubricant stuck to the brush roller 17 acan be applied to the photosensitive element 5 without any impact. Inother words, the lubricant does not cover the photosensitive element 5right after the application of the lubricant with the brush roller 17 a.However, the lubricant is spread by the pushing force of the cleaningblade 15 a when the photosensitive element 5 is passing under thecleaning blade 15 a , and the lubricant covers the photosensitiveelement 5. Therefore, the brush roller 17 a is made to rotate in thedirection of rotation of the photosensitive element 5 in order to applythe lubricant thereto without any impact. Furthermore, the peripheralspeed ratio (peripheral speed of photosensitive element/peripheral speedof brush roller) between the brush roller 17 a and the photosensitiveelement 5 ranges preferably from 0.8 to 1.2. If the peripheral speedratio is less than 0.8, the amount of supply of the lubricant isreduced, but if the peripheral speed ratio exceeds 1.2, thephotosensitive element 5 may be damaged by the impact, which may causethe life of the photosensitive element 5 to be reduced. Furthermore, inorder to supply the lubricant from the brush roller 17 a to thephotosensitive element 5 with less impact, the peripheral speed ratiobetween the brush roller 17 a and the photosensitive element 5 rangesmore preferably from 1.0 to 1.1.

The new-latent-image-carrier detector includes a storage unit such as anintegrated circuit (IC) chip that stores the use frequency of thephotosensitive element 5. The new-latent-image-carrier detector makesthe brush roller 17 a rotate for a fixed time with respect to thephotosensitive element 5 when the use frequency stored is zero (upon thefirst time use), and issues an instruction to the brush roller 17 a toapply the lubricant to a new photosensitive element 5. Although thenew-latent-image-carrier detector is configured to store the usefrequency of the photosensitive element 5 in the IC chip, a member thatis engaged with the main body 1 and disengaged therefrom only upon thefirst time use may be provided in the process cartridge 2A, and thefirst time use is detected by checking if the member is engaged with themain body 1. Alternatively, the new-latent-image-carrier detector may beconfigured as software that is stored in the lubricant applying unit 17.

Upon the first time use, the lubricant is applied to the photosensitiveelement 5 by the instruction of the new-latent-image-carrier detector,and the frictional coefficient of the photosensitive element 5 is set to0.4 or less, preferably 0.2 or less. By setting the frictionalcoefficient of the photosensitive element 5 to 0.4 or less, interactionbetween the photosensitive element 5 and toner is reduced, which allowsthe toner to be easily separated from the photosensitive element 5 andtransfer efficiency to be enhanced. This also allows the frictionbetween the cleaning blade 15 a and the photosensitive element 5 to besuppressed and cleaning efficiency to be enhanced. As for higherspherical toner in particular, since the toner becomes easy to roll onthe photosensitive element 5, occurrence of cleaning failure can besuppressed. By increasing transfer efficiency and reducing the amount oftoner to be cleaned, occurrence of cleaning failure due to long-term usecan be reduced. However, if the frictional coefficient becomes less than0. 1, the toner rolls too easily on the photosensitive element 5 and theamount of toner passing under the cleaning blade 15 a increases. This isnot preferable because cleaning failure may occur (see Example 1).

Upon the first time use, an application time of the lubricant by theinstruction of the new-latent-image-carrier detector, i.e., the time forrotating the brush roller 17 a is set to 100 seconds or more. By settingthe application time to 100 seconds or more, the frictional coefficientof the new photosensitive element 5 is reduced to obtain its saturatedstate (0.2 or less) (see Example 2).

Upon the first time use, a charging bias and a developing bias may be inan off state when the lubricant is applied by the instruction of thenew-latent-image-carrier detector. However, in order to more efficientlyapply the lubricant to the photosensitive element 5 without depositionof toner on the brush roller 17 a , a surface potential is applied tothe photosensitive element 5 and the developing sleeve, thus, preventingoccurrence of the surface stain. Therefore, the toner due to the surfacestain is prevented from entering the brush roller 17 a duringapplication of the lubricant.

As explained above, upon the first time use, the lubricant is applied,by the instruction of the new-latent-image-carrier detector, to the newphotosensitive element 5 to which no lubricant has been applied, andtherefore, a sufficient amount of the lubricant can be applied. In sucha manner, the lubricant is applied to the photosensitive element 5 uponthe first time use, and the frictional coefficient of the photosensitiveelement 5 is thereby reduced to become the saturated state. This allowsthe lubricant to be supplied to the photosensitive element 5 by thebrush roller 17 a because a low frictional coefficient can be maintainedeven if toner is stuck to the brush roller 17 a. Since the moldedlubricant 17 b is soft and loose, a new molded lubricant 17 b isprovided with a coating layer slightly harder than that of an internallubricant. However, by applying the lubricant upon the first time use,the coating layer can be efficiently removed. If the toner is stuck tothe brush roller 17 a , application efficiency of the lubricant from themolded lubricant 17 b to the photosensitive element 5 is reduced, whichcauses nonuniform application of the lubricant to occur on a portionwith toner deposited and a portion without toner on the photosensitiveelement 5. However, as explained in the embodiment, because thelubricant is applied to the photosensitive element 5 upon the first timeuse, uniform application of the lubricant thereto can be performed.Therefore, the frictional coefficient of the photosensitive element 5becomes uniform, and a rate of transfer of the toner image on thephotosensitive element 5 to the transfer paper P becomes uniform, whichallows an image with uniform density to be obtained. Furthermore, byapplying the lubricant upon the first time use and reducing thefrictional coefficient of the photosensitive element 5, even the tonerhaving a small particle size and high sphericity can be cleaned withoutreduction in cleaning efficiency.

The operation for image formation of the image forming apparatus isexplained below with reference to FIG. 3 and FIG. 4. Starting theoperation for image formation causes each of the photosensitive elements5 to rotate in clockwise, respectively. The surface of eachphotosensitive element 5 is uniformly charged by the charging roller 14a . The writing unit 6 radiates a laser beam corresponding to an imageof magenta onto the photosensitive element 5 of the process cartridge2A, a laser beam corresponding to an image of cyan onto thephotosensitive element 5 of the process cartridge 2B, a laser beamcorresponding to an image of yellow onto the photosensitive element 5 ofthe process cartridge 2C, and a laser beam corresponding to an image ofblack onto the photosensitive element 5 of the process cartridge 2D.Latent images respectively corresponding to image data of the colors areformed. When the latent images reach the respective positions of thedeveloping devices 10A, 10B, 10C, and 10D through rotation of eachphotosensitive element 5, the latent images are developed with toners ofmagenta, cyan, yellow, and black, respectively, to form a four-colortoner image.

On the other hand, the transfer paper P is fed from one of the paperfeed cassette 11 or 12 of the paper feed portion, and is conveyed by aregistration roller pair 59 at a timing at which the transfer paper Padequately meets each toner image formed on the photosensitive elements5. The registration roller pair 59 is provided right before the transferbelt 3 a. The transfer paper P is charged to a positive polarity by apaper attracting roller 58 provided near the entrance of the transferbelt 3 a, and is electrostatically attracted to the surface of thetransfer belt 3 a. The toner images of magenta, cyan, yellow, and blackare sequentially transferred to the transfer paper P while the transferpaper P attracted to the transfer belt 3 a is conveyed thereby, and afull color toner image with the four colors thereon is formed. At thistime, some of the toner is not transferred and remains on thephotosensitive elements 5. The transfer paper P is applied with heat andpressure by the fixing device 9, and the toner image on the transferpaper P is fused into place. Thereafter, the transfer paper P with theimage fixed passes through a paper discharging system according to amode specified, and is reversed and discharged onto the paper dischargetray 26 on the upper side of the main body 1, or passes through thereversing unit 8 from the fixing device 9 to be directly discharged.Alternatively, if the double-sided image forming mode is selected, thetransfer paper P is sent into the paper reverse conveying path 54 of thereversing unit 8 and switched back to be conveyed to the double-sidedunit 7, supplied again to an imaging portion provided with the processcartridges 2A, 2B, 2C, and 2D where an image is formed on the rearsurface of the transfer paper P, and is discharged.

Each of the photosensitive elements 5 that separate from the transferbelt 3 a continues rotation as it is, and the brush roller 17 a scrapesoff the lubricant from the molded lubricant 17 b and applies it to thephotosensitive element 5. The lubricant applied is pressed against thephotosensitive element 5 when the toner remaining on the photosensitiveelement 5 is cleaned with the cleaning blade 15 a, and thereby a coat isformed on the photosensitive element 5.

Thereafter, in the image formation, the processes of image formation arerepeated. However, the coat of the lubricant formed on thephotosensitive element 5 is very thin, and therefore, charging by thecharging unit 14 is not inhibited. After the processes, the toner imagedeveloped again on the photosensitive element 5 is transferred to thetransfer paper P attracted to the transfer belt 3 a.

The operation of the new-latent-image-carrier detector is explainedbelow with reference to FIG. 5. FIG. 5 is a flowchart of the operationof the new-latent-image-carrier detector. When power to the main body 1is turned on (step SI), the new-latent-image-carrier detector refers tothe use frequency of the photosensitive element 5 stored in the IC chip,and determines whether this is first time use of the photosensitiveelement 5 (use frequency is zero), i.e., whether the photosensitiveelement 5 is a new one (step S2 ). At step S2, when it is determinedthat the photosensitive element 5 is a new one (step S2, Yes (Y)), theprocess is branched to step S3, and the new-latent-image-carrierdetector issues an instruction to the main body 1 to apply the lubricantto the new photosensitive element 5. The main body 1 receives theinstruction and drives the photosensitive element 5 for a fixed time(100 seconds or more) to rotate the brush roller 17 a, and the lubricantis thereby scraped from the molded lubricant 17 b to be applied to thephotosensitive element 5. With the application, the frictionalcoefficient of the photosensitive element 5 is reduced to 0.4 or less(step S3). At step S3, it is desirable to operate the developing rollerand the transfer belt 3 a at the same linear velocity as that of thephotosensitive element 5, or to separate the two from the photosensitiveelement 5. When the application of the lubricant is finished, theprocess proceeds to step S4 where an ordinary warm-up operation isconducted. At step S2, if it is determined that this is not the firsttime use of the photosensitive element 5 (step S2, No (N)), the processskips step S3, and the ordinary warm-up operation is conducted (stepS4).

If a smaller volume-average particle size Dv of toner is used for theimage forming apparatus according to the embodiment, reproduction of athin line is improved. Therefore, toner having a particle size of 8micrometers or less at largest is used. However, if the particle size istoo small, developing capability and cleaning capability are reduced,and therefore, toner having a particle size of 3 micrometers or more atsmallest is preferable. Furthermore, if it is less than 3 micrometers,carrier or toner having a micro particle size that is not easy to bedeveloped is increased on the surface of the developing roller.Therefore, contact/friction of toner other than the toner with/againstcarrier becomes insufficient or the contact/friction thereofwith/against the developing roller becomes also insufficient, andreversely charged toner is thereby increased. Thus, an abnormal imagesuch as surface fog is formed, which is not preferable.

A particle size distribution expressed by a ratio (Dv/Dn) between thevolume-average particle size Dv and a number-average particle size Dnranges preferably from 1.00 to 1.40. By making the particle sizedistribution sharp, the distribution of an amount of charge on tonerparticles can be made uniform. If Dv/Dn exceeds 1.40, the distributionis widened and reversely charged toner is increased, and therefore, itis difficult to obtain high quality images. If Dv/Dn is less than 1.00,manufacture thereof is difficult, which is not practical. The tonerparticle size is obtained by measuring an average particle size of50,000 toner particles using a Coulter Counter Multisizer (manufacturedby Coulter Co.) and selectively using an aperture having a size of ahole for measurement of 50 micrometers corresponding to the particlesize of toner to be measured.

The shape factor SF-1 of toner ranges preferably from 100 to 180, theshape factor SF-2 thereof ranges preferably from 100 to 180. FIG. 6A andFIG. 6B are schematic diagrams of toner shapes. FIG. 6A is a diagram forexplaining the shape factor SF-1 and FIG. 6B is a diagram for explainingthe shape factor SF-2. The shape factor SF-1 indicates the degree ofsphericity of toner shape, and is expressed by the following expression(2). The shape factor SF-1 is a value obtained by dividing the square ofa maximum length MXLNG of a shape formed by projecting toner onto atwo-dimensional plane, by a shape area AREA, and by multiplying theresult by 100Π/4.SF−1={(MXLNG)²/AREA}×(100Π/4)  (2)If the value of SF-1 is 100, the shape of toner becomes perfectsphericity, and if the value of SF-1 is greater, the shape is moreirregular.

The shape factor SF-2 indicates the degree of irregularity of tonershape, and is expressed by the following expression (3). The shapefactor SF-2 is a value obtained by dividing the square of a peripherallength PERI of a shape formed by projecting toner onto a two-dimensionalplane, by the shape area AREA, and by multiplying the result by 100Π/4.SF−2={(PERI)²/AREA}×(100Π/4)  (3)If the value of SF-2 is 100, the surface of toner has no irregularity,and if the value of SF-2 is greater, the irregularity on the surface ofthe toner is more significant. The shape factor is measured specificallyby photographing toner with a scanning electron microscope (S-800:manufactured by Hitachi Ltd.), introducing the photograph into an imageanalyzer (LUZEX3: manufactured by Nireco Corp.), and analyzing andcalculating it.

If the shape of toner is more spherical, a contact between toner andtoner or between toner and the photosensitive element 5 becomes a pointcontact. Therefore, the attracting force between toner particles getsweak, and as a result, fluidity becomes high. The attracting forcebetween toner and the photosensitive element 5 gets weak, and as aresult, a transfer ratio becomes high, and reversely charged toner canbe easily recovered by a temporary container.

The shape factors SF-1 and SF-2 of toner are preferably 100 or more. IfSF-1 and SF-2 increase, the reversely charged toner increases, and thedistribution of charge amount of toner is widened, which causes the loadon the temporary container to increase. Therefore, it is preferable thatSF-1 do not exceed 180, and it is also preferable that SF-2 do notexceed 180.

FIG. 7A and FIG. 7B are schematic diagrams of outline shapes of toner.FIG. 7A is a diagram of external appearance of the toner and FIG. 7B isa cross section of the toner. As shown in FIG. 7A, the x axis indicatesa long axis r1 of the longest axis of the toner, the y axis indicates ashort axis r2 of the second longest axis, and the z axis indicates athickness r3 of the shortest axis, and there is a relation among them asfollows: long axis r1>short axis r2>thickness r3.

The toner has a substantially spherical shape indicated by a ratio(r2/r1) between the long axis and the short axis that ranges from 0.5 to1.0, and by a ratio (r3/r2) between the thickness and the short axisthat ranges from 0.7 to 1.0. If the ratio (r2/r1) between the long axisand the short axis is less than 0.5, the shape is close to an irregularshape, and the distribution of charge amount is widened, which is notpreferable. If the ratio (r3/r2) between the thickness and the shortaxis is less than 0.7, the shape is close to an irregular shape, and thedistribution of charge amount is widened, which is not preferable.Particular1y, if the ratio (r3/r2) between the thickness and the shortaxis is 1.0, the toner has a substantially spherical shape, and thedistribution of charge amount is narrowed, which is preferable. The sizeof toner so far was measured by observing the toner with a scanningelectron microscope (SEM) while changing an angle of a visual field.

The shape of toner can be controlled by manufacturing methods. Forexample, the toner obtained by a dry milling method has irregularitiesalso on the surface of the toner, and the toner shape is not fixed. Evenif the toner is obtained by the dry milling method, by applyingmechanical or thermal processing thereto, the shape of the toner can bemade almost perfect sphericity. In the other methods of manufacturingtoner, droplets are formed using a suspension polymerization method andan emulsion polymerization method. The toner made by these methods oftenhas a smooth surface and a shape close to perfect sphericity.Furthermore, by stirring toner particles during reaction in the solventand applying a shearing force thereto, the shape of toner can be formedin an oval.

The toner adequately used in the image forming apparatus according tothe embodiment is obtained by allowing toner material solution toundergo crosslinking reaction and/or extension reaction in an aqueoussolvent. The toner material solution is obtained by dispersing polyesterprepolymer having at least a functional group containing nitrogen atoms,polyester, a colorant, and a mold release agent, in an organic solvent.A schematic structure of the toner manufactured in the above manner isshown in FIG. 8. FIG. 8 is the schematic diagram of the toner. The tonerconsists of a binder resin and a colorant. The binder resin consists ofpolyester prepolymer and polyester cross-linked to each other. Anexternal additive imparting fluidity is externally added to the surfaceof the toner. However, in addition to the external additive, the tonermay contain a charge control agent for controlling the chargeability ofthe toner and a mold release agent for improving releasability for thefixing device. A material and a method of manufacturing toner areexplained below.

Polyester is obtained through a polycondensation reaction of apolyhydric alcohol compound with a polyvalent carboxylic acid compound.

Polyhydric alcohol compounds (PO) include dihydric alcohol, (DIO) andpolyhydric alcohols being not less than a trihydric alcohol (TO), anddihydric alcohol (DIO) alone or a mixture of dihydric alcohol (DIO) witha small amount of trihydric alcohol (TO) is preferable. Dihydric alcohol(DIO) includes alkylene glycol (e.g. ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,4-butanediol, and 1,6-hexanediol),alkylene ether glycols (e.g. diethylene glycol, triethylene glycol,dipropylene glycol, polyethylene glycol, polypropylene glycol, andpolytetramethylene ether glycol), alicyclic diols (e.g. 1,4-cyclohexanedimethanol, and hydrogenated bisphenol A), bisphenols (e.g. bisphenol A,bisphenol F, and bisphenol S), adducts of alkylene oxide of thealicyclic diols (e.g. ethylene oxide, propylene oxide, and butyleneoxide), and adducts of alkylene oxide of the bisphenols (e.g. ethyleneoxide, propylene oxide, and butylene oxide). Among these, alkyleneglycol having a carbon number from 2 to 12 and the adducts of alkyleneoxides of the bisphenols are preferable. The adducts of alkylene oxidesof the bisphenols and a combination of the adducts of alkylene oxides ofthe bisphenols and alkylene glycol having a carbon number from 2 to 12are particularly preferable. Polyhydric alcohols being not less thantrihydric alcohols (TO) include polyhydric aliphatic alcohols rangingfrom trihydric to octahydric alcohols and above (e.g. glycerol,trimethylolethane, trimethylolpropane, pentaerythritol, and sorbitol),phenols being not less than trivalent phenols (e.g. trisphenol PA,phenol novolak, and cresol novolak), and adducts of alkylene oxides ofthe polyphenols being not less than trivalent polyphenols.

Polyvalent carboxylic acid (PC) includes divalent carboxylic acid (DIC)and polyvalent carboxylic acid being not less than trivalent carboxylicacid (TC). The divalent carboxylic acid (DIC) alone and a mixture of thedivalent carboxylic acid (DIC) and a small amount of the polyvalentcarboxylic acid (TC) are preferable. The examples of divalent carboxylicacids (DlC) are alkylene dicarboxylic acids (e.g. succinic acid, adipicacid, and sebacic acid), alkenylene dicarboxylic acid (e.g. maleic acidand fumaric acid), and aromatic dicarboxylic acids (e.g. phthalic acid,isophthalic acid, terephthalic acid, and naphthalene dicarboxylic acid).Among these, the alkenylene dicarboxylic acid having a carbon numberfrom 4 to 20 and the aromatic dicarboxylic acids having a carbon numberfrom 8 to 20 are preferable. The examples of polyvalent carboxylic acidsbeing not less than trivalent carboxylic acid (TC) are aromaticpolyvalent carboxylic acids having a carbon number from 9 to 20 (e.g.trimellitic acid and pyromellitic acid). The acid anhydrides or loweralkyl esters of these (e.g. methyl ester, ethyl ester, and isopropylester) may be used as polyvalent carboxylic acid (PC) and allowed toreact with the polyhydric alcohol (PO).

The ratio between the polyhydric alcohol (PO) and the polyvalentcarboxylic acid (PC) is an equivalent ratio [OH]/[COOH] between ahydroxyl group [OH] and a carboxyl group [COOH] and is generally from2/1 to 1/1, preferably from 1.5/1 to 1/1, more preferably from 1.3/1 to1.02/1.

The polycondensation reaction of polyhydric alcohol (PO) and polyvalentcarboxylic acid (PC) is performed by heating them to 150° C. to 280° C.in the presence of a known esterification catalyst such astetrabutoxytitanate and dibutyltin oxide, and by distilling watergenerated while pressure is reduced if required, and polyester havingthe hydroxyl group is obtained. A valence of the hydroxyl group ofpolyester is preferably 5 or more, and an acid value of polyestergenerally ranges from 1 to 30, preferably 5 to 20. By making polyesterhave the acid value, it is easy to be negatively charged, and affinitybetween a recording paper and toner becomes excellent when the toner isfixed on the recording paper. Thus, low-temperature fixability isimproved. However, if the acid value exceeds 30, polyester has adeteriorating tendency of charge stability, particularly ofenvironmental fluctuations.

The weight average molecular weight ranges from 10,000 to 400,000, andpreferably, 20,000 to 200,000. If the weight average molecular weight isless than 10,000, offset resistance is worsened, which is notpreferable. If the weight average molecular weight exceeds 400,000, thelow-temperature fixability gets worse, which is not preferable.

It is preferable to contain urea-modified polyester in polyester, inaddition to unmodified polyester obtained through the polycondensationreaction. The urea-modified polyester is obtained by reacting a carboxylgroup or a hydroxyl group at the end of polyester obtained through thepolycondensation reaction with a polyvalent isocyanate compound (PIC) toobtain polyester prepolymer (A) having an isocyanate group, and byreacting the polyester prepolymer (A) with amine group to crosslinkand/or extend a molecular chain.

Examples of polyvalent isocyanate compounds (PIC) are aliphaticpolyvalent isocyanates (e.g. tetramethylene diisocyanate, hexamethylenediisocyanate, and 2,6-diisocyanate methyl caproate), alicyclicpolyisocyanates (e.g. isophorone diisocyanate and cyclohexylmethanediisocyanate), aromatic diisocyanates (e.g. tolylene diisocyanate anddiphenylmethane diisocyanate), aromatic aliphatic diisocyanates (e.g.α,α,α′,α′-tetramethylxylylene diisocyanate), isocyanates, compoundsformed by blocking of these polyisocyanates by a phenol derivative, anoxime, and a caprolactam, and a combination of at least two of these.

A ratio of the polyvalent isocyanate compound (PIC) is an equivalentratio [NCO]/[OH] of an isocyanate group [NCO] and a hydroxyl group [OH]of a polyester and is generally ranges from 5/1 to 1/1, preferably from4/1 to 1.2/1, and more preferably from 2.5/1 to 1.5/1. If the ratio of[NCO]/[OH] exceeds 5, the low-temperature fixability gets worse. If themole ratio of [NCO] is less than 1, when urea unmodified polyester isused, the urea content in the ester becomes low, thereby affecting hotoffset resistance.

The content of the polyvalent isocyanate compound (PIC) in the polyesterprepolymer (A) having an isocyanate group ranges generally from 0.5 wt.%to 40 wt. %, preferably from 1 wt. % to 30 wt. %, and more preferablyfrom 2 wt. % to 20 wt. %. If the content of the polyvalent isocyanatecompound is less than 0.5 wt. %, the hot offset resistance deterioratesand it is unfavorable from the viewpoint of compatibility of heatresistant preservability and low-temperature fixability. On the otherhand, if the content of the polyvalent isocyanate compound exceeds 40wt. %, the low-temperature fixability gets worse.

The number of isocyanate groups contained per molecule in the polyesterprepolymer (A) having the isocyanate group is generally at least 1,preferably, an average ranging from 1.5 to 3, and more preferably, anaverage ranging from 1.8 to 2.5. If the isocyanate group per molecule isless than 1, then the molecular weight of the urea-modified polyesterbecomes low and the hot offset resistance deteriorates.

Further, examples of amines (B) caused to react with the polyesterprepolymer (A) are a divalent amine compound (B1), a polyvalent aminecompound (B2) being not less than trivalent amines, aminoalcohol (B3),aminomercaptan (B4), amino acid (B5), and a compound (B6) in which theamino groups from the B1 to the B5 are blocked.

Examples of the divalent amine compound (B1) are aromatic diamines (e.g.phenylene diamine, diethylene diamine, and 4,4′-diaminodiphenylmethane), alicyclic diamines (e.g.4,4′-diamino-3,3′-dimethyidicyclohexylmethane, diamine cyclohexane, andisophorone diamine), and aliphatic diamines (e.g. ethylene diamine,tetramethylene diamine, and hexamethylene diamine). Examples of thepolyvalent amine compound (B2) being not less than trivalent amines arediethylene triamine and triethylene tetramine. Examples of theaminoalcohol (B3) are ethanolamine and hydroxyethylaniline. Examples ofthe aminomercaptan (B4) are aminoethyl mercaptan and aminopropylmercaptan. Examples of the amino acid (B5) are aminopropionic acid andaminocaproic acid. Examples of the compound (B6) in which the aminogroups from the B1 to the B5 are blocked are ketimine compounds obtainedfrom the amines from the B1 to the B5. ketones (e.g. acetone, methylethyl ketone, and methyl isobutyl ketone), and oxazolidine compounds.The preferable amines among the amines (B) are the B1 and a mixture ofthe B1 with a small amount of the B2.

A ratio of amines (B) is an equivalent ratio [NCO]/[NHx] of anisocyanate group [NCO] in the polyester prepolymer (A) having anisocyanate group and an amine group [NHx] in the amines (B), and rangesgenerally form 1/2 to 2/1, preferably from 1.5/1 to 1/1.5, and morepreferably from 1.2/1 to 1/1.2. If the ratio of [NCO]/[NHx] is greaterthan 2 or less than 1/2, the molecular weight of the urea-modifiedpolyester decreases and the hot offset resistance deteriorates.

Moreover, an urethane bond may be contained together with an urea bondin the urea-modified polyester. A mole ratio of the urea bond contentand the urethane bond content ranges generally from 100/0 to 10/90,preferably from 80/20 to 20/80, and more preferably from 60/40 to 30/70.If the mole ratio of the urea bond is less than 10%, the hot offsetresistance deteriorates.

The urea-modified polyester is manufactured by a method like a one-shotmethod. A polyhydric alcohol (PO) and a polyvalent carboxylic acid (PC)are heated up to 150° C. to 280° C. in the presence of a knownesterification catalyst such as tetrabutoxy titanate and dibutyltinoxide. The pressure is reduced if necessary and the water generated isremoved by evaporation to obtain polyester having a hydroxyl group.Further, polyvalent isocyanate (PIC) is allowed to react with thepolyester at a temperature of 40° C. to 140° C. to obtain polyesterprepolymer (A) having an isocyanate group. Furthermore, amines (B) areallowed to react with this polyester prepolymer (A) at a temperature of0° C. to 140° C. to obtain an urea-modified polyester.

If necessary, a solvent can be used for reaction of the polyvalentisocyanate (PIC) and reaction of the polyester prepolymer (A) with theamines (B). Examples of the solvent that can be used are aromaticsolvents (e.g. toluene and xylene), ketones (e.g. acetone, methyl ethylketone, and methyl isobutyl ketone), esters (e.g. ethyl acetate), amides(e.g. dimethyl formamide, and dimethyl acetoamide), and ethers (e.g.tetrahydrofuran) that are inert to the polyvalent isocyanate (PIC).

For crosslinking reaction and/or extension reaction of polyesterprepolymer (A) with amines (B), a reaction terminator can be used ifnecessary to adjust the molecular weight of the urea-modified polyesterthat is obtained. Examples of the reaction terminator are monoamines(e.g. diethylamine, dibutylamine, butylamine, and laurylamine) andcompounds in which these are blocked (ketimine compounds).

The weight average molecular weight of the urea-modified polyester isgenerally not less than 10,000, preferably ranges from 20,000 to10,000,000, and more preferably from 30,000 to 1,000,000. If the weightaverage molecular weight is less than 10,000, the hot offset resistancedeteriorates. The number average molecular weight of the urea-modifiedpolyester is not particularly restricted when the unmodified polyesteris used, and may be a number average molecular weight that is suitableto obtain the weight average molecular weight. If the urea-modifiedpolyester is used alone, the number average molecular weight rangesgenerally from 2,000 to 15,000, preferably from 2,000 to 10,000, andmore preferably from 2,000 to 8,000. If the number average molecularweight is greater than 20,000, the low-temperature fixability and thegloss, if the urea-modified polyester is used for a full color unit, areworsened.

By using both the unmodified polyester and the urea-modified polyester,the low-temperature fixability and the gloss, if both of them are usedfor the full color unit, are improved. Therefore, it is preferable touse them together rather than using the urea-modified polyester alone.The unmodified polyester may contain polyester modified by a chemicalbond other than the urea bond.

It is preferable that the unmodified polyester and the urea-modifiedpolyester be at least partly compatible from the viewpoint of thelow-temperature fixability and the hot offset resistance. Therefore, itis preferable that the unmodified polyester and the urea-modifiedpolyester have similar composition.

A weight ratio of the unmodified polyester and the urea-modifiedpolyester ranges generally from 20/80 to 95/5, preferably from 70/30 to95/5, and more preferably from 75/25 to 95/5. The most preferable weightratio ranges from 80/20 to 93/7. If the weight ratio of theurea-modified polyesters is less than 5 %, the hot offset resistancedeteriorates, and compatibility of heat resistant preservability andlow-temperature fixability gets worse.

A glass transition point (Tg) of a binder resin containing unmodifiedpolyester and urea-modified polyester ranges generally from 45° C. to65° C., preferably from 45° C. to 60° C. If the glass transition pointis below 45° C., then the heat resistance of the toner deteriorates,while if the glass transition point is above 65° C., the low-temperaturefixability becomes insufficient.

The urea-modified polyester tends to be present on the surface of tonerbase particles obtained, and therefore, even if the glass transitionpoint is lower as compared with that of the known polyester based toner,it has a tendency to have good heat resistant preservability.

For colorant, known dyes and pigments can be used. For example,followings and mixtures thereof can be used: carbon black, Nigrosinedye, ion black, Naphthol Yellow S, Hansa Yellow (10G, 5G, G), cadmiumyellow, yellow iron oxide, yellow ocher, chrome yellow, titanium yellow,polyazo yellow, oil yellow, Hansa Yellow (GR, A, RN, R), pigment yellowL, Benzidine Yellow (G, GR), Permanent Yellow (NCG), Vulcan Fast Yellow(5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anthrazane Yellow BGL,Isoindolinone Yellow, red ion oxide, minium, red lead, Cadmium Red,Cadmium Mercury Red, Antimony Vermilion, Permanent Red 4R, Para Red,Fire Red, parachloro-ortho-nitroaniline red, Lithol Fast Scarlet G,Brilliant Fast Scar1et, Brilliant Carmine BS, Permanent Red (F2R, F4R,FRL, FRLL, F4RH), Fast Scar1et VD, Vulcan Fast Rubin B, BrilliantScarlet G, Lithol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B,Pigment Scarlet 3B, Bordeaux 5B, Toluidine Maroon, Permanent BordeauxF2K, Helio Bordeaux BL, Bordeaux 10B, BON Maroon Light, BON MaroonMedium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake,Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone Red,Pyrazolone Red, Polyazo Red, Chrome Vermilion, Benzidine Orange,Perinone Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkali BlueLake, Peacock Blue Lake, Victoria Blue Lake, metal-free PhthalocyanineBlue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC),indigo, ultramarine blue, Prussian blue, Anthraquinone Blue, Fast VioletB, Methyl Violet Lake, Cobalt Violet, Manganese Violet, Dioxane Violet,Anthraquinone Violet, Chrome Green, Zinc Green, chrome oxide, pyridian,Emerald Green, Pigment Green B, Naphthol Green B, Green Gold, Acid GreenLake, Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green,titanium oxide, zinc white, and lithopone. The content of the colorantis generally from 1 wt. % to 15 wt. %, preferably from 3 wt. % to 10 wt.%, based on total weight of the toner.

The colorant can be also used as a master batch which is prepared bycombining the colorant with a resin. Examples of the binder resin formanufacturing the master batch or being kneaded with the master batchare styrene polymers and substituted styrene polymers such aspolystyrene, poly-p-chlorostyrene, and polyvinyltoluene; copolymers ofone of these and a vinyl compound; and polymethyl methacrylate,polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate,polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin,polyurethane, polyamide, polyvinyl butyral, polyacrylic resin, rosin,modified rosin, terpene resin, aliphatic or alicyclic hydrocarbon resin,aromatic petroleum resin, chlorinated paraffin, and paraffin waxes.These resins can be used alone or in combination.

Known charge control agents can be used as a charge control agent.Examples of the charge control agent are Nigrosine based dyes,triphenylmethane based dyes, chromium-containing complex dyes, chelatemolybdate pigments, Rhodamine based dyes, alkoxy amines, and quaternaryammonium salts (including fluorine modified quaternary ammonium salts),alkylamides, simple substances of phosphorous or compounds thereof,simple substances of tungsten or compounds thereof, fluorine-basedactive agents, salicylic acid metal salts, and metal salts of salicylicacid derivatives. More specific examples of the charge control agent areBontron 03 as a Nigrosine based dye, Bontron P-51 as a quaternaryammonium salt, Bontron S-34 as a metal containing azo dye, E-82 as anoxynaphthoe acid based metal complex, E-84 as a salicylic acid basedmetal complex, E-89 as a phenol based condensate (these are manufacturedby Orient Chemical Industries, Ltd.), TP-302 and TP-415 as quaternaryammonium salt molybdenum complexes (manufactured by Hodogaya ChemicalIndustries, Ltd.), Copy Charge PSY VP2038 as a quaternary ammonium salt,Copy Blue PR as a triphenylmethane derivative, Copy Charge NEG VP2036and Copy Charge NX VP434 as quaternary ammonium salts (these aremanufactured by Hoechst Co., Ltd.), LRA-901 and LR-147 as a boroncomplex (manufactured by Japan Carlit Co., Ltd.), copper phthalocyanine,perylene, quinacridone, azo based pigments, and polymer compounds havinga functional group such as a sulfonic acid group, a carboxyl group, andquaternary ammonium salt. Among these, materials that control tonernegatively are particularly preferable.

The amount of use of the charge control agent is determined depending onthe type of binder resins, presence or absence of additives to be usedas required, and a method of manufacturing toner including a dispersionmethod, and therefore, it is not uniquely restricted. However, thecharge control agent is used in a range from 0.1 to 10 parts by weight(wt. parts), preferably from 0.2 to 5 wt. parts per 100 wt. parts of thebinder resin. If it exceeds 10 wt. parts, the toner is charged toohighly, effects of the main charge control agent are decreased, andelectrostatic attracting force for a developing roller is increased,which causes fluidity of the developer to be lowered and image densityto be reduced.

A wax having a low melting point in a range from 50° C. to 120° C.functions effectively between the fixing roller and the surface of toneras a mold release agent during dispersion with a binder resin. Due tothis function of wax, there is no need to apply a mold release agentlike oil to the fixing roller to improve high temperature offset.Examples of waxes are vegetable based wax such as carnauba wax, cottonwax, Japan tallow, rice wax; animal based wax such as bees wax andlanolin; mineral based waxes such as ozokerite and cercine; andpetroleum based wax such as paraffin, micro crystalline, and petrolatum.Other examples of wax apart from these natural waxes are synthetichydrocarbon wax such as Fischer Tropsch wax, polyethylene wax; andsynthetic wax such as esters, ketones, and ethers. Furthermore, thefollowings can also used: fatty acid amides of 12-hydroxy stearic acidamides, stearic acid amides, phthalic anhydride imide, and chlorinatedhydrocarbon; and crystalline high polymers having a long alkyl group ina side chain such as homopolymers or copolymers (e.g. copolymers ofn-stearyl acrylate-ethyl methacrylate) of polyacrylates such aspoly-n-stearyl methacrylate, poly-n-lauryl methacrylate, that arecrystalline high polymer resins having a low molecular weight.

These charge control agent and the mold release agent can be melted andkneaded with master batch and binder resin, or may be added to anorganic solvent when it is dissolved or dispersed.

The external additive is used for helping fluidity, development, andcharging of toner particles, and inorganic particles are preferably usedas the external additive. The primary particle size of the inorganicparticles is preferably from 5×10−3 to 2 micrometers, more preferablyfrom 5×10−3 to 0.5 micrometer. A specific surface area based on the BETmethod is preferably from 20 m2/g to 500 m2/g. A proportion of theinorganic particles to be used is preferably from 0.01 wt. % to 5 wt. %,more preferably from 0.01 wt. % to 2.0 wt. % of the total weight of thetoner.

Specific examples of the inorganic particles are silica, alumina,titanium oxide, barium titanate, magnesium titanate, calcium titanate,strontium titanate, zinc oxide, tin oxide, quartz sand, clay, mica,wollastonite, silious earth, chrome oxide, cerium oxide, red oxide,antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate,barium carbonate, calcium carbonate, silicon carbide, and siliconnitride. Among these, as a fluidity imparting agent, a combination of ahydrophobic silica particle and a hydrophobic titanium oxide particle ispreferable. In particular, if a combination of these each of which hasan average particle size of not greater than 5×10⁻² micrometer is usedand mixed, electrostatic force and Van der Waals force with toner aresignificantly improved. Therefore, even if toner is mixed and agitatedin a developing device to obtain a desired charged level, the fluidityimparting agent is not separated from the toner, which allows excellentimage quality without image defects such as “white spots” to beobtained. In addition, toner particles remaining on an image carriereven after an toner image is transferred can be reduced.

Titanium oxide particles are excellent in environmental stability andimage density stability. On the other hand, charge rise characteristictends to be worse. Therefore, if the amount of addition of titaniumoxide particles is greater than that of silica particles, influence ofthe side effect becomes more significant. However, if the amount ofaddition of hydrophobic silica particles and hydrophobic titanium oxideparticles is in a range from 0.3 wt. % to 1.5 wt. %, the charge risecharacteristic is not lost so much, and desired charge risecharacteristic is obtained. Thus, a stable image quality is obtainedeven if copying is repeatedly carried out.

A method of manufacturing toner is explained below. The method explainedhere is a preferable method, but the method is not limited thereto.

1) A toner material solution is prepared by dispersing a colorant,unmodified polyester, polyester prepolymer having an isocyanate group,and a mold releasing agent in an organic solvent.

The organic solvent has preferably a volatile organic solvent having aboiling point below 100° C. because it is easy to be removed after tonerbase particles are formed. Specific examples of the organic solvent aretoluene, xylene, benzene, carbon tetrachloride, methylene chloride,1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene,chloroform, monochlorobenzene, dichloroethylidene, methyl acetate, ethylacetate, methyl ethyl ketone, methyl isobutyl ketone. These can be usedalone or a combination of at least two of them. Particularly, aromaticsolvents such as toluene and xylene, and halogen hydrocarbons such asmethylene chloride, 1,2-dichloroethane, chloroform, and carbontetrachloride are preferable. The amount of use of the organic solventranges generally from 0 to 300 wt. parts per 100 wt. parts of thepolyester prepolymer, preferably from 0 to 100 wt. parts, and morepreferably from 25 to 70 wt. parts.

2) The toner material solution is emulsified in an aqueous medium in thepresence of a surfactant and fine particles of resin.

The aqueous medium may be water alone or may contain an organic solventsuch as an alcohol (e.g. methanol, isopropyl alcohol, and ethyleneglycol), dimethyl formamide, tetrahydrofuran, a cellosolve group (e.g.methyl cellosolve), and a lower ketone group (e.g. acetone, and methylethyl ketone).

The amount of use of the aqueous medium per 100 wt. parts of the tonermaterial solution ranges generally from 50 to 2,000 wt. parts,preferably from 100 to 1,000 wt. parts. If the amount is less than 50wt. parts, this affects the dispersion of the toner material solution,and toner particles of a predetermined particle size cannot be obtained.It is not economical to use the aqueous medium if the amount exceeds2,000 wt. parts.

Further, to improve the dispersion in the aqueous medium, a dispersingagent such as a surfactant and fine particles of resin is added asrequired. Examples of the surfactant are anionic surfactants such asalkyl benzene sulfonate, (α-olefin sulfonate, and ester phosphate; aminesalts such as alkyl amine salts, aminoalcohol fatty acid derivatives,polyamine fatty acid derivatives, and imidazoline; cationic surfactantsof quaternary ammonium salt types such as alkyl trimethyl ammoniumsalts, dialkyl dimethyl ammonium salts, alkyl dimethyl benzyl ammoniumsalts, pyridinium salts, alkyl isoquinolinium salts, and benzethoniumchloride; nonionic surfactants such as fatty acid amide derivatives andpolyhydric alcohol derivatives; and ampholytic surfactants such asalanine, dodecyl di (aminoethyl)glycine, di (octylaminoethyl)glycine,N-alkyl-N, and N-dimethyl ammonium betaine.

Furthermore, by using a surfactant having a fluoroalkyl group, a desiredeffect can be achieved with a very small amount thereof. Preferableexamples of anionic surfactants having a fluoroalkyl group arefluoroalkyl carboxylic acids having a carbon number from 2 to 10 andtheir metal salts, disodium perfluorooctane sulfonyl glutamate, sodium3-[ω-fluoroalkyl (C6 to C11)oxy]-1-alkyl (C3 to C4)sulfonate, sodium3-[ω-fluoroalkanoyl (C6 to C8)-N-ethylamino]-1-propane sulfonate,fluoroalkyl (C11 to C20) carboxylic acid and its metal salts,perfluoroalkyl carboxylic acid (C7 to C13) and its metal salts,perfluoroalkyl (C4 to C12)sulfonic acid and its metal salts,perfluorooctane sulfonic acid diethanolamide,N-propyl-N-(2-hydroxyethyl)perfluorooctane sulfonamide, perfluoroalkyl(C6 to C10)sulfonamidepropyl trimethyl ammonium salts, perfluoroalkyl(C6 to C10)-N-ethylsulfonyl glycine salts, monoperfluoroalkyl (C6 toC16)ethyl phosphoric acid esters.

Examples of trade names are SURFLON S-111, S-112, S113 (manufactured byAsahi Glass Co., Ltd.), FLUORAD FC-93, FC-95, FC-98, FC-129(manufactured by Sumitomo 3M Co., Ltd.), UNIDINE DS-101, DS-102(manufactured by Daikin Industries, Ltd.), MEGAFACE F-110, F-120, F-113,F-191, F-812, F-833 (manufactured by Dainippon Ink & Chemicals, Inc.),EKTOP EF-102, 103, 104, 105, 112, 123A, 123B, 306A, 501, 201, 204(manufactured by Tochem Products Co., Ltd.), and FTERGENT F-100 and F150(manufactured by Neos Co., Ltd.).

Examples of cationic surfactants are primary aliphatic, secondaryaliphatic, or secondary amino acid having a fluoroalkyl group;quaternary aliphatic ammonium salts such as perfluoroalkyl (C6 toC10)sulfonamidepropyl trimethyl ammonium salt; benzalkonium salts,benzethonium chloride, pyridinium salts, and imidazolinium salts. Theexamples of trade names thereof are SURFLON S-121 (manufactured by AsahiGlass Co., Ltd.), FLUORAD FC-135 (manufactured by Sumitomo 3 M Co.,Ltd.), UNIDINE DS-202 (manufactured by Daikin Industries, Ltd.),MEGAFACE F-150 and F-824 (manufactured by Dainippon Ink & Chemicals,Inc.), EKTOP EF-132 (manufactured by Tochem Products Co., Ltd.), andFTERGENT F-300 (manufactured by Neos Co., Ltd.).

The fine particles of resin are added to stabilize toner base particlesthat are formed in the aqueous medium. Therefore, it is preferable toadd the fine particles of resin so that a coverage of the fine particlesover the surface of the toner base particles is in a range of 10 % to 90%. Examples of the fine particles are fine particles of poly methylmethacrylate having a particle size of 1 micrometer and 3 micrometers;fine particles of polystyrene having a particle size of 0.5 micrometerand 2 micrometers; and fine particles of poly (styrene-acrylonitrile)having a particle size of 1 micrometer. Examples of trade names arePB-200H (manufactured by Kao Corp.), SGP (manufactured by Soken Co.,Ltd.), TECHPOLYMER-SB (manufactured by Sekisui Plastics Co., Ltd.),SGP-3G (manufactured by Soken Co., Ltd.), and MICROPEARL (manufacturedby Sekisui Fine Chemical Co. Ltd.). Moreover, inorganic dispersingagents such as calcium phosphate tribasic, calcium carbonate, titaniumoxide, colloidal silica, and hydroxyapatite can also be used.

Dispersion droplets may be stabilized by a high polymer protectivecolloid as a dispersing agent that can be used with both fine particlesof resin and an inorganic dispersing agent. Examples are acids such asacrylic acid, methacrylic acid, (α-cyanoacrylic acid, α-cyanomethacrylicacid, itaconic acid, crotonic acid, fumaric acid, maleic acid, or maleicanhydride; or (metha)acrylic monomers containing a hydroxyl group suchas β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropylacrylate, β-hydroxypropyl methacrylate, γ-hydroxypropyl acrylate,γ65-hydroxypropyl methacrylate, 3-chloro 2-hydroxypropyl acrylate,3-chloro 2-hydroxypropyl methacrylate, diethylene glycol monoacrylicester, diethylene glycol monomethacrylic ester, glycerol monoacrylicester, glycerol monomethacrylic ester, N-methylol acrylamide, N-methylolmethacrylamide; vinyl alcohol or ethers of vinyl alcohol such as vinylmethyl ether, vinyl ethyl ether, vinyl propyl ether; or esters ofcompounds that contains a vinyl alcohol and a carboxyl group such asvinyl acetate, vinyl propionate, vinyl butyrate; acrylamide,methacrylamide, diacetone acrylamide or their methylol compounds; acidchlorides such as acryloyl chloride and methacryloyl chloride;homopolymers or copolymers of a compound having a nitrogen atom orheterocyclic ring thereof such as vinylpyridine, vinylpyrrolidone,vinylimidazole, and ethyleneimine; polyoxyethylene compounds such aspolyoxyethylene, polyoxypropylene, polyoxyethylene alkyl amine,polyoxypropylene alkyl amine, polyoxyethylene alkyl amide,polyoxypropylene alkyl amide, polyoxyethylene nonyl phenyl ether,polyoxyethylene lauryl phenyl ether, polyoxyethylene stearyl phenylester, and polyoxyethylene nonyl phenyl ester; and a cellulose groupsuch as methyl cellulose, hydroxyethyl cellulose, and hydroxypropylcellulose.

A dispersion method is not particularly limited, and it is possible touse known facilities of a low-speed shearing type, a high-speed shearingtype, a friction type, a high-pressure jetting type, and an ultrasonicdispersion type. Among these, to allow the dispersed particles to havean average particle size ranging from 2 to 20 micrometers, thehigh-speed shearing type is preferred. When a high-speed shearing typedispersing machine is used, the number of revolutions is notparticularly limited and is generally from 1,000 revolutions per minute(rpm) to 30,000 rpm, preferably from 5,000 rpm to 20,000 rpm. Thedispersion time is not particularly limited and is generally from 0.1 to5 minutes in a batch system. The dispersing temperature is generallyfrom 0° C. to 150° C. (under a pressure), preferably from 40° C. to 98°C.

3) While preparing an emulsified liquid, amines (B) are added and areallowed to react with polyester prepolymer (A) having an isocyanategroup.

This reaction is also performed with cross linkage and/or extension of amolecular chain. The reaction time is selected according to thereactivity of amines (B) with an isocyanate group structure of thepolyester prepolymer (A), and is generally in a range from 10 minutes to40 hours, preferably in a range from 2 hours to 24 hours. The reactiontemperature ranges generally from 0° C. to 150° C., preferably from 40°C. to 98° C. Moreover, a known catalyst can be used if necessity.Specific examples of the catalyst are dibutyl tin laurate and dioctyltin laurate.

4) After completion of the reaction, the organic solvent is removed froma mixture emulsified and dispersed (reaction compound), is washed, anddried to obtain the toner base particles.

To remove the organic solvent therefrom, the whole system is graduallyheated up while laminar flow is stirred. The mixture is stirredvigorously at around a particular temperature, a solvent is removed fromthe mixture, and then fusiform toner base particles are prepared.Further, if a compound like calcium phosphate salt that dissolves in anacid or an alkali is used an a dispersion stabilizer, after the calciumphosphate salt is dissolved in an acid like hydrochloric acid, thecalcium phosphate salt is removed from the toner base particles by amethod of cleaning. In addition, the calcium phosphate salt may bedecomposed by an enzyme and removed.

5) A charge controlling agent is implanted into the toner base particlesthus obtained, and inorganic fine particles such as those of silica andtitanium oxide are added externally to obtain the toner.

The implantation of the charge controlling agent and the externaladdition of the inorganic fine particles are carried out by a knownmethod using a mixer and so on. Thus, toner having a small particle sizeand a sharp particle size distribution can be obtained easily. Moreover,by vigorously stirring in the process of removing the organic solvent,the shape of particles between a perfectly spherical shape and a rugbyball-like shape can be controlled. Furthermore, the morphology of thesurface can also be controlled between the smooth and the rough.

FIG. 9 is a diagram of the result of experiments in which stablecleaning performance can be obtained by adding the inorganic additive tothe lubricant. Toner manufactured by the method of manufacturing tonerand having a volume-average particle size of 5 micrometers is used. Themolded lubricant 17 b is added with 30 wt. % of silica for zinc stearateas a main component, and it is evaluated how the charging roller 14 agets soiled by changing the particle size of silica to various particlesizes. The soil of the charging roller 14 a represents the amount oftoner remaining on the surface of the photosensitive element 5 withoutbeing cleaned by the cleaning blade 15 a, and this amount is thought asa typical property of the cleaning performance of the image formingapparatus. Soil rank 5 indicates that no soil is found on the chargingroller 14 a, and the soil of the charging roller 14 a is getting worseas the rank is lowered. In this evaluation, if the rank is 4 or higher(ranks 4 and 5), no defects occur in an image to be transferred to atransfer paper P. Therefore, it is understood from FIG. 9 that nodefects occurs if a particle size of silica to be added ranges from 0.01to 0.5 micrometer. The similar experiments were conducted using tonerhaving different particle sizes. By adding silica having a particle sizethat satisfies the expression (1) to the molded lubricant 17 b , stablecleaning performance is obtained.

FIG. 10 is a graph of a relationship between the number of sheets ofA4-sized transfer paper P passed through a space with a newphotosensitive element 5 and a frictional coefficient of thephotosensitive element 5. The transfer paper P has an image with animage area of 5% formed thereon and passed through the space with thenew photosensitive element 5 to which the lubricant is not applied.According to the graph, the frictional coefficient of the newphotosensitive element 5 is 0.4 or more, but is gradually decreasingwith an increase in the number of sheets to which images aretransferred. The frictional coefficient decreases to 0.2 or less whenimages are transferred to about 100 sheets, where the frictionalcoefficient is saturated. It is understood from this that the frictionalcoefficient of the photosensitive element 5, after the lubricant isapplied thereto by the instruction of the new-latent-image-carrierdetector, is preferably 0.4 or less, more preferably 0.2 or less.

The frictional coefficient of the photosensitive element 5 was measuredby an oiler belt system in the following manner. FIG. 11 is a diagramfor explaining how to measure the frictional coefficient of thephotosensitive element 5. In this case, a belt 70 was stretched on drumcircumference ¼ of the photosensitive element 5 so that a fine paperhaving an intermediate thickness was directed in a longitudinaldirection. A load 71 of, for example, 0.98 N (100 g) was hung at one endof the belt 70, and a force gage 72 was placed on the other end andstretched. The load was read at a point in time when the belt 70 wasmoved, and a value read was substituted in the following expression:frictional coefficient μs=2/Π×ln (F/0.98) (where p: static frictionalcoefficient, and F: value measured) to calculate the frictionalcoefficient.

FIG. 12 is a graph of a relationship between the rotation time of thephotosensitive element 5 and the frictional coefficients (at threepoints) of the photosensitive element 5 when the new photosensitiveelement 5 is made to rotate alone under the following condition and thelubricant is applied thereto by the brush roller 17 a.

Conditions: Photosensitive element Diameter: 30 Linear velocity: 125mm/s Molded lubricant Material: Zinc stearate Spring pressure force:1000 mN Brush roller Material: Conductive nylon Density: 30 K F/inch²Thickness: 10 D Engaging amount against photosensitive element: 1.0 mm

According to FIG. 12, by setting the application time to 100 seconds ormore, it is possible to reduce the frictional coefficient of thephotosensitive element 5 to obtain its saturated state (0.2 or less).

Since the present invention is configured as explained above, it ispossible to provide the lubricant capable of significantly reducing theamount of toner, as compared with the conventional technology, thatpasses under the cleaning blade and remains on the photosensitiveelement irrespective of states of an image formed even if sphericaltoner is used, and also to provide the lubricant applying unit, theprocess cartridge, and the image forming apparatus.

Furthermore, it is possible to provide the lubricant applying unit, theprocess cartridge, and the image forming apparatus capable ofmaintaining stable cleaning performance by supplying the sufficientamount of lubricant to the photosensitive element even if it is thefirst time use of the photosensitive element.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. A lubricant for electrophotography applied to a latent image carrierto which toner having a sphericity of equal to or more than 0.94 issupplied, wherein an inorganic additive is added to the lubricant, andthe inorganic additive satisfies2Y/1000≦X≦Y/10 where Y is a particle size of the toner in micrometer,and X is a particle size of the inorganic additive in micrometer.
 2. Thelubricant according to claim 1, wherein the inorganic additive is asubstance containing at least one of silica, titania, alumina, magnesia,zirconia, ferrite, and magnetite.
 3. The lubricant according to claim 1,wherein a main component of the lubricant is either of fatty acid metalsalt and fluorine particles.
 4. The lubricant according to claim 3,wherein an amount of addition of the inorganic additive ranges from 1weight percent to 30 weight percent with respect to the main component.5. A lubricant applying unit that applies a lubricant forelectrophotography to a latent image carrier, the lubricant applyingunit comprising a brush roller that rotates around a rotational axis,and is in contact with the latent image carrier, wherein toner having asphericity of equal to or more than 0.94 is supplied to the latent imagecarrier, an inorganic additive is added to the lubricant, the inorganicadditive satisfies2Y/1000≦X≦Y/10 where Y is a particle size of the toner in micrometer,and X is a particle size of the inorganic additive in micrometer, thelubricant is a molded lubricant that is molded as a solid block, and thebrush roller slides along, and scrapes off the molded lubricant so thatthe lubricant is applied to the latent image carrier.
 6. The lubricantapplying unit according to claim 5, further comprising anew-latent-image-carrier detector that detects whether the latent imagecarrier is used for a first time, wherein when it is detected that thelatent image carrier is used for the first time, the lubricant isapplied to the latent image carrier.
 7. The lubricant applying unitaccording to claim 6, wherein a frictional coefficient of the latentimage carrier after applying the lubricant is equal to or less than 0.4.8. The lubricant applying unit according to claim 5, further comprisinga pushing unit that pushes the molded lubricant against the brush rollerby a force of equal to or more than 200 meter-Newtons.
 9. The lubricantapplying unit according to claim 5, wherein the brush roller rotates ina direction of rotation of the latent image carrier, and a peripheralspeed ratio of the brush roller to the latent image carrier ranges from0.8 to 1.2.
 10. A process cartridge comprising: a latent image carrier;at least one of a charging unit that causes a charging member to contactor to be close to the latent image carrier to charge the latent imagecarrier; a developing unit that deposits toner on a latent image on thelatent image carrier to develop the latent image with the toner; and acleaning unit that cleans the toner remaining on the latent imagecarrier with a cleaning blade; and a lubricant applying unit thatapplies a lubricant for electrophotography to the latent image carrier,the lubricant applying unit including a brush roller that rotates arounda rotational axis, and is in contact with the latent image carrier,wherein toner having a sphericity of equal to or more than 0.94 issupplied to the latent image carrier, an inorganic additive is added tothe lubricant, the inorganic additive satisfies2 Y/ 1000≦ X≦Y/10 where Y is a particle size of the toner in micrometer,and X is a particle size of the inorganic additive in micrometer, thelubricant is a molded lubricant that is molded as a solid block, and thebrush roller slides along, and scrapes off the molded lubricant so thatthe lubricant is applied to the latent image carrier.
 11. An imageforming apparatus comprising a process cartridge that includes a latentimage carrier; at least one of a charging unit that causes a chargingmember to contact or to be close to the latent image carrier to chargethe latent image carrier; a developing unit that deposits toner on alatent image on the latent image carrier to develop the latent imagewith the toner; and a cleaning unit that cleans the toner remaining onthe latent image carrier with a cleaning blade; and a lubricant applyingunit that applies a lubricant for electrophotography to the latent imagecarrier, the lubricant applying unit including a brush roller thatrotates around a rotational axis, and is in contact with the latentimage carrier, wherein toner having a sphericity of equal to or morethan 0.94 is supplied to the latent image carrier, an inorganic additiveis added to the lubricant, the inorganic additive satisfies2Y/1000≦X≦Y/10 where Y is a particle size of the toner in micrometer,and X is a particle size of the inorganic additive in micrometer, thelubricant is a molded lubricant that is molded as a solid block, and thebrush roller slides along, and scrapes off the molded lubricant so thatthe lubricant is applied to the latent image carrier.
 12. The imageforming apparatus according to claim 11, wherein the toner has avolume-average particle size ranging from 3 micrometers to 8micrometers; and a ratio of a volume-average particle size to anumber-average particle size ranging from 1.00 to 1.40.
 13. The imageforming apparatus according to claim 11, wherein the toner has a shapefactor SF-1 ranging from 100 to 180; and a shape factor SF-2 rangingfrom 100 to
 180. 14. The image forming apparatus according to claim 11,wherein the toner is substantially spherical.
 15. The image formingapparatus according to claim 11, wherein the toner has a shape definedby a long axis r1, a short axis r2, and a thickness r3, where r1≧r2≧r3,a ratio r2/r1 ranges from 0.5 to 1.0, and a ratio r3/r2 ranges from 0.7to 1.0.
 16. The image forming apparatus according to claim 11, whereinthe toner is obtained by subjecting a toner material solution to eitherone or both of crosslinking reaction and extension reaction in anaqueous medium, the toner material solution being obtained by dispersingat least polyester prepolymer having a functional group containing anitrogen atom, polyester, a colorant, and a mold release agent into anorganic solvent.
 17. An image forming apparatus comprising a lubricantapplying unit that applies a lubricant for electrophotography to alatent image carrier, wherein the lubricant applying unit includes abrush roller that rotates around a rotational axis, and is in contactwith the latent image carrier, toner having a sphericity of equal to ormore than 0.94 is supplied to the latent image carrier, an inorganicadditive is added to the lubricant, the inorganic additive satisfies2Y/1000≦X≦Y/10 where Y is a particle size of the toner in micrometer,and X is a particle size of the inorganic additive in micrometer, thelubricant is a molded lubricant that is molded as a solid block, and thebrush roller slides along, and scrapes off the molded lubricant so thatthe lubricant is applied to the latent image carrier.
 18. The imageforming apparatus according to claim 17, wherein the toner has avolume-average particle size ranging from 3 micrometers to 8micrometers; and a ratio of a volume-average particle size to anumber-average particle size ranging from 1.00 to 1.40.
 19. The imageforming apparatus according to claim 17, wherein the toner has a shapefactor SF-1 ranging from 100 to 180; and a shape factor SF-2 rangingfrom 100 to
 180. 20. The image forming apparatus according to claim 17,wherein the toner is substantially spherical.
 21. The image formingapparatus according to claim 17, wherein the toner has a shape definedby a long axis r1, a short axis r2, and a thickness r3, where r1≧r2≧r3,a ratio r2/r1 ranges from 0.5 to 1.0, and a ratio r3/r2 ranges from 0.7to 1.0.
 22. The image forming apparatus according to claim 17, whereinthe toner is obtained by subjecting a toner material solution to eitherone or both of crosslinking reaction and extension reaction in anaqueous medium, the toner material solution being obtained by dispersingat least polyester prepolymer having a functional group containing anitrogen atom, polyester, a colorant, and a mold release agent into anorganic solvent.